PhD Vermeiren Lieve Compleet - Hogeschool Gent

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The ability of lactic acid to rotate under influence of polarised light results in the existence of two stereo-isomers being the L(+) (levorotary) and D(-) (dextrorotary) form. If there is a mixture of both, it is termed racemic (DL) (Bogaert & Naidu, 2000; Carr et al., 2002). The production of L(+) or D(-) isomers varies with the genus and species within a genus of LAB (Stiles & Holzapfel, 1997; Liu, 2003) and depends on the stereo-specificity of the present lactate dehydrogenase (Kandler & Weiss, 1986). From a nutritional point of view, D(-)-lactate in food is undesirable because it is not readily metabolised in humans compared with L(+)lactate (Liu, 2003). It has been demonstrated that the antimicrobial activity of lactic acid is stereo-specific and it seems that micro-organisms are least sensitive to the isomer they intrinsically produce. Listeria monocytogenes is a L-lactic acid producer and is therefore more sensitive to D-lactic acid than to L-lactic acid. However, this difference in sensitivity is less than the strain variation in L-lactic acid sensitivity indicating that the stereo-specific activity of lactic acid has no practical importance regarding L. monocytogenes. 1.5.1.2. Hydrogen peroxide In the presence of oxygen, LAB can produce hydrogen peroxide (H2O2). Its formation occurs through electron transport and is catalysed by the flavin enzyme NADH-oxidase. Furthermore, H2O2 can be synthesised from pyruvate, α-glycerophosphate and even from lactate. Accumulation of H2O2 can also result from dismutation of superoxide anions (O2 - ) by the action of a superoxide dismutase that is present in most LAB or by Mn-ions that are present in the cytoplasm of bacteria lacking superoxide dismutase (De Vuyst & Vandamme, 1994a). In general, LAB are catalase negative (Kandler & Weiss, 1986). Since the produced H2O2 cannot be hydrolysed, it accumulates in the growth medium where it can exert its action. However, a few species, including L. sakei, have been reported to possess a hemedependent catalase (Hertel et al., 1998). Ito et al. (2003) showed that H2O2, accumulated by LAB in a cell suspension, is very effective in reducing the counts of several food born pathogens. The bactericidal effect of H2O2 is mainly attributed to its peroxidising properties on the membrane lipids, causing increased membrane permeability, and on other basic molecular structures, e.g. nucleic acids and cell proteins (Piard & Desmazeaud, 1991). Furthermore, H2O2 may react further to produce additional inhibitory compounds, e.g. the generation of hypothiocyanite by the action of lactoperoxidase on H2O2 and thiocyanate (De Vuyst & Vandamme, 1994a). Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 11
1.5.1.3. Carbon dioxide Carbon dioxide (CO2) is mainly produced by heterofermentative LAB from hexoses (Kandler & Weiss, 1986). Furthermore, various LAB can produce CO2 from malate and citrate (Hugenholtz, 1993) and also by metabolising arginine via the arginine deiminase pathway (Arena et al., 1999). Finally, decarboxylation of amino acids can also be a minor source of CO2 (Urbach, 1995). Carbon dioxide contributes to the antagonistic activity of LAB (De Vuyst & Vandamme, 1994a) and its inhibitory properties are due to its role in creating an anaerobic environment, its extracellular and intracellular pH-decreasing effect and specific actions on enzymes and membranes (Devlieghere, 2000). 1.5.1.4. Diacetyl Diacetyl, the characteristic flavour associated with butter and cheese, is synthesised from pyruvate aerobically as well as anaerobically by citrate fermenting LAB (Hugenholtz, 1993; Liu, 2003). In the presence of citrate and a metabolisable energy source (e.g. in milk), the production of excessive amounts of pyruvate can result in the production of diacetyl and acetoin. When hexoses are the only fermentable carbon source, no diacetyl and little if any acetoin is produced. Diacetyl has antimicrobial activities but Gram-negative bacteria, yeasts and moulds are more sensitive to diacetyl than Gram-positive bacteria and usually high levels are necessary for inhibition (De Vuyst & Vandamme, 1994a). Its mode of action is believed to be due to interference with the utilisation of arginine. Diacetyl is rarely produced at sufficient levels to make a major contribution to the antimicrobial activity of LAB (Piard & Desmazeaud, 1991; De Vuyst & Vandamme, 1994a). 1.5.1.5. Acetaldehyde and ethanol Acetaldehyde, responsible for the typical aroma of yoghurt, is produced during the carbohydrate metabolism of heterofermentative LAB, principally L. delbrueckii subsp. bulgaricus, and further reduced to ethanol by an alcohol dehydrogenase. When the latter enzyme is absent or repressed, it may result in the excretion of acetaldehyde. The possible antagonistic effect of acetaldehyde is poorly documented and existing data suggest that this compound plays a minor antagonistic role (Piard & Desmazeaud, 1991; De Vuyst & Vandamme, 1994a). Similarly, although ethanol may be produced by LAB, the produced levels are so low that its contribution to the antimicrobial activity of LAB is minimal (Caplice & Fitzgerald, 1999). Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 12
Page 1: Hogeschool Gent Biopreservation of
Page 4 and 5: ir. Lieve Vermeiren Biopreservation
Page 6 and 7: Woord vooraf Proefbuizen, labojasse
Page 8: Table of contents
Page 11 and 12: 3.4. EFFECT OF PROTECTIVE LAB ON TH
Page 13 and 14: 1. INTRODUCTION....................
Page 15 and 16: 2.8. STATISTICAL ANALYSES 189 3. RE
Page 18 and 19: Introduction and objectives In rece
Page 20 and 21: • Sub-objective 5 Chapter 5 aimed
Page 22: Summary
Page 25 and 26: Chapter 3 presented a systematic st
Page 27 and 28: 10A and an atmosphere containing 50
Page 30: Samenvatting
Page 33 and 34: werden deze stammen beschouwd als m
Page 35 and 36: ewaartemperatuur (4°C versus 7°C)
Page 37 and 38: In-vitro testen toonden aan dat de
Page 40 and 41: Chapter 1 Antagonistic micro-organi
Page 42 and 43: esides lactic acid, including carbo
Page 44 and 45: 1.4.3. The genus Pediococcus This g
Page 46 and 47: taxonomy) and the present phylogene
Page 48 and 49: 1.5.1. Fermentation end-products 1.
Page 52 and 53: 1.5.2. Bacteriocins Bacteriocins, p
Page 54 and 55: molecule inserts into the membrane
Page 56 and 57: 1.5.3. Other antagonistic systems 1
Page 58 and 59: explains why CMP, immediately after
Page 60 and 61: Weissella Weissella viridiscens has
Page 62 and 63: 2.3.3.3. Discolouration Green disco
Page 64 and 65: eported an incidence of L. monocyto
Page 66 and 67: The use of micro-organisms or their
Page 68 and 69: 3.2.2. Organic acids In general, re
Page 70 and 71: Furthermore, protective LAB can be
Page 72 and 73: Fish, fish products and seafood Spo
Page 74 and 75: Table 1.3. Effect of (non-)bacterio
Page 76 and 77: performance as a biopreservative in
Page 78 and 79: Table 1.6. Studies on the effect of
Page 80 and 81: prevent them from growth of food bo
Page 82 and 83: The application of the host-specifi
Page 84 and 85: Multiplicity of infection (MOI) Pha
Page 86 and 87: using Leuc. carnosum 4010 in frankf
Page 88 and 89: activity of LAB in general, this se
Page 90 and 91: effect (Gram et al., 2002). Several
Page 92 and 93: for one or more of these vitamins o
Page 94 and 95: clinical cases, patients were immun
Page 96 and 97: different degrees and classify them
Page 98: this way an equal distribution over
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Chapter 2 Evaluation of meat born l
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temperatures, the characterisation
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dextranicum LMG 6908 T , Leuc. carn
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2.6. Behaviour of 12 selected putat
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considered as unacceptable. Finally
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From the 74 remaining strains, only
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Among the isolates, 76% (28/37) was
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Within the group of isolated strain
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with fast growth rates at low tempe
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pH 6.3 6.2 6.1 6.0 5.9 5.8 5.7 0 5
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34th day of the storage period, alt
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Table 2.5. Summary of the LAB-count
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Chapter 3 In-vitro and in-situ grow
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1. Introduction A considerable part
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7°C and revived by transferring a
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The sensory quality of cooked ham s
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lesser extent compared to the LAB s
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LC2 and LM3 not significantly decre
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Sensory rejection was mainly based
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log10(cfu/g), respectively. It migh
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Chapter 4 Co-culture experiments de
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1. Introduction Interest in the rol
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growth characteristics, antibacteri
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1 g/l Peptone (Oxoid)) was prepared
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were sensitive to 8/11 tested antib
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Log10(cfu/g) Log10(cfu/g) 9 8 7 6 5
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On the other hand, no significant (
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Table 4.3. Evolution of the glucose
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Log10(cfu/g) Log10(cfu/g) 9 8 7 6 5
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day 28 in the HG-product. However,
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glucose. Buchanan & Bagi (1997) als
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Chapter 5 The interaction of the no
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1. Introduction Several authors hav
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(3) an interaction study at 7°C be
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3. Results and discussion The chemi
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Log10(cfu/g) 9 8 7 6 5 4 3 2 1 0 0
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Clearly, the growth of L. sakei 10A
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Table 5.2. Evolution of the pH of t
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Chapter 6 The sensory acceptability
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1. Introduction During the last dec
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mixture of Leuc. mesenteroides LM2
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to a sensory panel of 18 non-traine
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inoculation, 200 g portions of prod
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Buffering capacity (mmol lactic aci
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where LAB-growth results in sensory
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3.2.1. Antagonistic activity of L.
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In all five products, L. sakei 10A
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the glucose consumption in 10A-samp
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In general, CMP with such low pH-va
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3.3. Discussion 3.3.1. Antagonistic
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that cooked ring sausages were deem
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Chapter 7 The contribution of lacti
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1. Introduction The last two decade
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Table 7.1. Composition of the diffe
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In all three experiments, growth of
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2.5.2. Challenge experiment in CFS
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3. Results and discussion 3.1. Co-c
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However, cell numbers were analysed
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Log10(cfu/ml) or pH Log10(cfu/ml) o
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Log10(cfu/ml) Log10(cfu/ml) 10 9 8
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Log10(cfu/ml) Log10(cfu/ml) 9 8 7 6
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that case the pH of the CFS would h
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Log10(cfu/ml) Log10(cfu/ml) 9 8 7 6
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these experiments when there was st
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Chapter 8 Treatment with bacterioph
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1. Introduction Listeria monocytoge
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(7°C and 30°C). Experiments were
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L. monocytogenes cocktail, 100 µl
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3. Results and discussion 3.1. Effe
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susceptibility of the genus Listeri
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end-point for the microbial shelf-l
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therefore, be sufficient to control
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contaminated cooked meat products,
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General discussion, conclusions and
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possible that the bacteriocin was n
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manufactured cooked meat products (
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deviations can be prevented and led
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List of abbreviations
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pfu plaque forming unit PPS Pepton
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References 1. Aasen, I.M., Markusse
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26. Berry, E.D., Liewen, M.B., Mand
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50. Buncic, S., Avery, S.M. & Moorh
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75. Devlieghere, F., Debevere, J. &
Page 282 and 283:
99. Foegeding, P.M., Thomas, A.B.,
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125. Hudson, J.A., Billington, C.,
Page 286 and 287:
150. Korkeala, H., Alanko, T., Mäk
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174. Marceau, A., Zagorec, M. & Cha
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nonbacteriocinogenic Carnobacterium
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style green olive fermentations. Ap
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253. Stratford, M. (2000). Traditio
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277. Vitas, A.I. & Garcia-Jalon, V.
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Curriculum vitae Curriculum vitae L
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of Listeria monocytogenes by the no
Page 304 and 305:
2. ILSI Europe 2nd International Sy
Page 306:
13. EFSA Colloquium On Microorganis
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PhD Vermeiren Lieve Compleet - Hogeschool Gent

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